The C3H/10T1/2C18, line is one of the major cell lines used for in vitro oncogenesis studies. We shall investigate how these non-muscle cells are converted into functional muscle cells by micromolar concentrations of the cancer chemotherapeutic agents, 5-azacytidine as well as 5-aza-2'-deoxycytidine. The incorporation of these analogs into DNA will be studied and the extent and possible localization of this incorporation correlated with the biological action of the drugs. The effect of azacytidine substitution on the physical structure of DNA and its ability to serve as a template for RNA polymerase will be investigated. Most of the experiments will be performed using biologically active concentrations of 5-azacytidine and 5-aza-2'-deoxycytidine and short treatments of synchronized cells will also be used. Biochemical characterization of the C3H/10T1/2C18 line will be performed to explain the type and extent of phenotypic conversion occurring. The effect of 5-azacytidine on other cells including oncogenically transformed C3H/10T1/2C18 cells and also some differentiated cell types will be examined to assess the universality of the phenomenon. The possibility that other differentiated cells are induced in C3H/10T1/2C18 cells by 5-azacytidine will also be examined. These studies should more fully characterize the effects of the aza-nucleosides and yield information not only on molecular mechanisms of differentiation but also possibly on the oncogenic transformation produced by the same concentrations of 5-azacytidine.